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https://issues.apache.org/jira/browse/HBASE-29857?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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rstest updated HBASE-29857:
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Attachment: TestBucketCacheEmptyPersistenceBug.java
> BucketCache fails to start when persistence file was written with empty cache
> -----------------------------------------------------------------------------
>
> Key: HBASE-29857
> URL: https://issues.apache.org/jira/browse/HBASE-29857
> Project: HBase
> Issue Type: Bug
> Components: regionserver
> Affects Versions: 2.6.3
> Reporter: rstest
> Priority: Major
> Attachments: TestBucketCacheEmptyPersistenceBug.java
>
>
> When a RegionServer with BucketCache persistence enabled is restarted, if the
> BucketCache was empty at shutdown time, the new RegionServer fails to start
> with a `NullPointerException` in `BucketCache.parsePB()`.
>
> The bug is in the interaction between `BucketProtoUtils.serializeAsPB()` and
> `BucketCache.retrieveChunkedBackingMap()`:
> 1. During shutdown with empty cache: When `backingMap.size() == 0`,
> `serializeAsPB()` writes `numChunks = 0` to the persistence file, but the
> loop that writes `BucketCacheEntry` objects never executes (because there are
> no entries to iterate). This means **no BucketCacheEntry is written to the
> file
> 2. During startup: `retrieveChunkedBackingMap()` reads `numChunks = 0` from
> the file, but still attempts to read the first chunk using
> `parseDelimitedFrom()`. Since no `BucketCacheEntry` was written,
> `parseDelimitedFrom()` returns `null`.
> 3. NPE occurs: The null `firstChunk` is passed to `parsePB()`, which calls
> `firstChunk.getDeserializersMap()` on the null object, causing NPE.
>
> This bug just make the region server not able to be restarted.
> Use the attached test can reproduce this bug. Put it under
> `hbase-server/src/test/java/org/apache/hadoop/hbase/io/hfile/TestBucketCacheEmptyPersistenceBug.java`
> and run it.
>
>
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